The core density of the defects in perovskite thin films will directly affect the properties of perovskite solar cells. On the other hand, interface engineering is usually being used to effectively improve the quality of perovskite thin films. In this sought of work, MAPbI3 perovskite thin films were modified by an antisolvent process using trioctylphosphine as a passivator. Trioctylphosphine is a kind of Lewis base and from the experimental results, it is noticed on being contribute to MAPbI3 grain growth and grain boundary passivation. Due to the grain boundary passivation and grain size increase, the intense defect density inside the grain and at the grain boundary of the MAPbI3 films is gradually reduced, thereby improving the carrier lifetime, while the hydrophobic property of octyl alkane makes the perovskite thin films less susceptible to air, water and oxygen degraded by the influence. The solar cell which are using the proposed films with the device structure configuration as ITO/SnO2/MAPbI3/spiro-OMeTAD/Ag and the perovskite layers were modified with trioctylphosphine. Among them, the perovskite thin films showcased to have a best performance when the trioctylphosphine chlorobenzene solution was about 0.15% and the PCE of the device reached for about 12.17%, an increase of 10% was compared with the standard device. In addition, the modified device exhibits good environmental stability, retaining about 90% of the initial efficiency for 100 h in a 70% humidity environment. •The modification of MAPbI3 perovskite films by trioctylphosphine, which can improve the performance of the solar cell.•The results show that trioctylphosphine as a Lewis base contributes to grain growth and grain boundary passivation.•The hydrophobic properties of octyl alkanes make perovskite films less susceptible to degradation by oxygen and water.•0.15% of trioctylphosphine chlorobenzene solution is the best ratio. The PCE reaches 12.17%.•After being exposed to a humidity of 70% for 100 h, the device only experiences a 90% decrease in PCE.